Issue with BS 6700

[EnOm]

Hi,
I have a question regarding using BS 6700:1997 to size water pipes. My issue is as follows:

on page 30, under (2.5-Pipe sizing) it states
The system shall be designed and installed so that the design flow rates given in table 3 shall be available at each outlet and any group of outlets where the total demand does not exceed 0.3 l/s, when only that outlet or group of outlets are open"
In the standard there also exists Annex D, which has Loading Unit values for different fixtures and their equivalent flow rates. The chart starts at 10 Load Units.

My problem is that I'm facing a case that falls in between these two.
Considering only cold water supply:
I have a wash room with 3 wash basins.
Loading Units for wash basin (cold) = 1.5 LU (Table D.1, page 72)
Design Flow Rate for wash basin (cold) = 0.15 l/s (Table 3, page 30)
By using Loading Units: Cold Water Loading Units = 3 x 1.5 = 4.5 Loading Units which is outside the range of the chart provided.
By adding up design flow rate: 3 x 0.15 = 0.45 l/s which is more than the 0.3 l/s under which table 3 can be used.

Thoughts?

Best Regards

 

[PEDARRIN2]

I am not familiar with the British Standard so i am not sure there is a counterpart to what i am thinking.

We have two charts which we use, one for flow on systems including flush valve fixtures and one for flows not including flush valve fixtures. The former starts at 5 fixture units and the latter starts at 1 fixture unit. I think load units might be similar to fixture units. A lavatory or wash basin would be 1 fixture unit for me and 1.5 load units for you. So obviously the lavatories are less than the chart.

Could there be a counterpart chart for the non flush valve system? If so, it should have the flow values you are looking for.

For us, piping to three lavatories would be sized for ~3.5 gpm. That is assuming each receives 2 gpm separately.

 

[EnOm]

PEDARRIN2,
Thank you for your response.
I am familiar with what you are talking. I've went through the ASPE Vol 2 before and took a look at the curves and tables there. But I think you are using updated versions of those since I think they are quite old (~1920s).
From the data in ASPE:
cold water supply for 3 private lavatories gives (3 x 0.5 FUs) = 1.5 FUs. This translates to approximately 4 gpm.

 

[PEDARRIN2]

The Hunter's curves are old and used higher flows than presently allocated.

ASPE is looking at revising the curves to compensate for current use profiles and flows.

But until they (or somebody) provides guidance, I generally compensate by using a 0.6 to 0.8 factor, depending on the type of facility. So if the curve calls for 4 gpm, I use 2.4-3.2 gpm.

 

[EnOm]

PEDARRIN2,
Thank you for your help

Regards